A typical turbomachine has a housing, a rotor shaft carrying at least one impeller, a bearing assembly having at least one active magnetic bearing supporting the rotor shaft in the housing, at least one gap sensor and a controller connected to the gap sensor for controlling the active magnetic bearing. In order to make it possible to precisely determine position with the gap sensor, a target interacting with the gap sensor is is provided on the rotor shaft.
Magnetic bearings operate without contact and thus wear and are therefore suitable to a special extent for rapidly turning installations such as turbomachines. A gap remains between the rotor parts and confronting stator parts of the magnetic bearing, which gap is to be kept as constant as possible. In particular direct contact due to tilting, impact, or the like must be avoided. In the case of an active magnetic bearing the rotor position is therefore continuously monitored by the gap sensor and restoring forces are then supplied by a corresponding actuation of the magnetic bearing to force the rotor, that is the rotor shaft, back into a desired position.
In order to make possible a constant position determination with the gap sensor, a target interacting with the gap sensor is provided on the rotor shaft and must be provided during manufacture of the rotor shaft.
With turbomachines in practice fine disk packs that are attached during manufacture of the rotor shaft are generally used as a target. To this end the disk packs are preassembled, premachined, shrunk onto the rotor shaft and then finely machined down to the outer diameter of the rotor shaft. The interaction of the disk unit and the gap sensor produces a signal depending on the spacing and thus the precise position of the shaft is determined. This approach has proven useful in practice. The production expenditure and thus the production costs are high, however, and the outer diameter of the rotor shaft is increased by the assembly of the disk unit.